Process for manufacturing paperboard with high grease resistance by applying a plurality of starch coatings to a wet board



Nov. 26, 1968 A. J. AYCOCK ET AL 3,413,190

PROCESS FOR MANUFACTURING PAPERBOARD WITH HIGH GREASE RESISTANCE BYAPPLYING A PLURALITY or STARCH COATINGS TO A WET BOARD Filed Dec. 30,1964 2 Sheets-Sheet l SHOWER SECONDARY PWE HERD Box A O 8 8\d 2 TH\RD\ 2PRESS SECOND BREAKER mgT SECOND SMOOTHING kH-NRD STACK PRESS PRESS messDRYER SECTIONS FIRST DRYER secnou ALBERT J. HYCOCK Cr- HENRY G: BOOTH\NVENTORS PRlMARY HERD BOX K W) FOURDPAMER T ORNEYS Nov. 26, 1968 A. J.AYcocK ET AL 3,413,190

PROCESS FOR MANUFACTURING PAPERBOARD WITH HIGH GREASE RESISTANCE BYAPPLYING A PLURALITY OF STARCH COATINGS TO A WET BOARD Filed Dec. 30,1964 2 Sheets-Sheet (g snm w x K 0 5 U s2 & ,,U 0000000 DE d) J 9 PE U-[110 KW DRYER SECT \ON ALBERT J. AYCOCK 6* HENRY G. BOOTH INVENTORS-:cxg 53 5 7 19m H0215 ATTORN YS United States Patent 3,413,190 PROCESSFOR MANUFACTURING PAPERBOARD WITH HIGH GREASE RESISTANCE BY APPLY- IN-GA PLURALITY 0F STARCH COATINGS TO A WET BOARD Albert J. Aycoek and HenryG. Booth, Augusta, Ga., assignors to Continental Can Company, Inc., NewYork, N.Y., a corporation of New York Filed Dec. 30, 1964, Ser. No.422,195 1 Claim. (Cl. 162-175) ABSTRACT OF THE DISCLOSURE A process formanufacturing paperboard having high grease resistance wherein aplurality of starch coatings are applied to the surface of thepaperboard sheet, the first of the coatings being applied at the breakerstack which is before the application of any other surface coatmgs.

This invention relates to a product and a process for manufacturingpaperboard and more specifically to a product and a process forobtaining a board which is substantially impervious to greases, oils,and the like.

Packaging and container materials maintain a predominant position in oureconomy. The range of materials employed in this field vary from metalcontainers and packaging material to metal foils, metal coated papersand plastics, coated papers and paperboards, etc. Throughout thisspecification, the term packaging or packag ing material will be used todenote any type of material or container employed to contain or house,singly or in bulk, whether hot or cold, liquids, paste, semi-solids,solids or gases.

The requirement for packaging materials vary greatly. Of paramountinterest, is the selection of the best material with the least cost. Inmany instances, the cost of the packaging material may exceed the costof its contents. In this instance, increased emphasis would be appliedto reduce the cost of the packaging material or container so that thecontainer represents only a small fraction of the total cost of thearticle. Due to the increased popularity of the throw-away container,greater economies must be effected for the packaging of these productssince the container is used only once for its intended purpose.

This invention relates to a product and a process for the manufacturingof paperboard which may be utilized, due to its high resistance togrease, oils, other liquids, etc. as a packaging material for thesematerials or for compositions containing these materials. In the past,the use of metal packaging material has dominated the field due to theinability of greases, oils, etc. to penetrate to the metal. However,metal containers are relatively expensive and attempts have been made toreplace the use of metal containers with coated papers and paperboard.Early attempts employed a type of combination metal and paperboardwherein a thin coat of metal or foil was deposited in some manner on oneside of the paperboard so that the paperboard would lend rigidity to thecontainer while the metal contributed the impervious quality. Thismethod considerably reduced the cost of the packaging material but wasnot entirely satisfactory due to the inherent problems concerned withthe bonding of two dissimilar materials.

Further attempts were directed to the preparation of packaging materialsconstructed solely of paper or paperboard along with suitable coatingswhich were applied to the paperboard during or immediately after itsmanufacture. The coatings were designed to contribute the imperviousquality required for the use of packaging mate- "Ice rials utilized inthe fields of packaging greases, oils, hot beverages, etc. Many suchtypes of coatings were employed and none were found to be entirelysatisfactory. Coatings which were impervious to the aforementionedproducts were expensive and thus undesirable from an economic viewpoint.Although inexpensive, many other coatings retained their imperviousnessfor only a short period of time and thus were undesirable from a qualitystandpoint. Many such coatings which were employed in the manufacture ofpaper and paperboard container materials included coatings of polyvinylalcohol, polyester resins, waxes, latex, stearto-chromic chloride,various fabric sizes and coatings of starch.

This invention relates to the application of starch coatings topaperboard to produce high grease resistance materials and although theapplication of starch coatings to paperboard is known in the art, theproduction of high grease resistant materials has not been achieved. Thepresent invention sets forth a novel manner in which the starch coatingsare applied which yields truly unexpected results.

The term grease will be employed throughout the specification to denotegreases, oils, turpentines, hot beverages, and the like.

Accordingly, it is the principal object of the present invention toimprove the grease resistance of packaging and container materials.

It is a further object of the present invention to improve the greaseresistance of materials constructed of coated paperboard.

It is a further object of the present invention to provide a greaseresistant material of coated paperboard wherein the principal ingredientof the coating is starch.

It is a further object of the present invention to provide a greaseresistant material of coated paperboard wherein coatings of starch areapplied to the paperboard at selected steps or points in the manufacturethereof.

It is still a further object of the present invention to provide aprocess for manufacturing grease resistant paperboard wherein coatingsof starch are applied at selected steps or points to the paperboardduring the manufacturing process.

The manufacturing of a routine grade of paperboard, e.g., a coated coldwaxing, bleached paperboard, is well known in the art. Further, it isknown to apply starch coatings and other materials during certain stepsin the manufacture of paperboard possessing some grease resistance. Inthe past, these coatings have usually been applied at the size press orthe wet calenders. However, the paperboard produced according to thatprocess, did not possess the high grease resistance which is requiredfor many applications. This invention relates to the application of ahigh solids (approximately 20% solids) cooked starch paste at the stepsin the process heretofore unknown. In the usual operation, after the wetpaperboard passes from the wire it is advanced through a series ofpresses and dryers at which time it then enters a breaker stack wherethe paperboard sheet is compacte and levelled. Just prior to the entryof the sheet at the nip of the breaker stack, a high solids cookedstarch paste of approximately 20% solids is applied to the top or uppersurface or, alternatively to the lower or bottom surface, of the sheetof paperboard so that a pool of the starch paste is on the surface ofthe sheet as the sheet enters the nip of the breaker stack. At thatpoint, there is approximately one to one and one-half pounds of cookedstarch solids applied to one thousand square feet of the surface of thesheet. The high solids starch is impressed into the surface of the sheetby the breaker stack at a point in the process where the sheet ofpaperboard is still relatively wet and absorbent. After further drying,sizing, and again drying, the sheet enters the wet calenders wherecoatings are applied to both the top and bottom surfaces of the sheet.The bottom surface receives a coating of low solids starch mixed with asodium alginate solution which increases the water holding capacity ofthe starch and increases the ability of the starch solution to form afilm. The top surface of the sheet receives a second coat of high solidsstarch by the use of a waterbox at the wet calender. Thereafter, a firstcoater is employed to apply a third coating of high solids starch to thetop surface of the paperboard sheet. From then on, the remaining stepsare conventional in that the sheet is polished, regular pigmentedcoatings are applied, the sheet is again polished and after advancementthrough the dry calenders is advanced to a reel where it is rolled aboutthe reel. Although many of the steps in the process set forth are known,this invention relates to the application of a high solids starch to thepaperboard at the breaker stack which is before the application of anyother coatings and to the further application of a high solids starchcoating at the wet calenders and the first coater.

The invention both as to its organization and method of operationtogether with further objects and advantages thereof will best beunderstood by reference to the following specification taken inconjunction with the accompanying drawings in which:

FIGURE 1 is a flow diagram showing the formation of a sheet ofpaperboard from the primary headbox through the breaker stack; and

FIGURE 2, when positioned end-to-end with the FIG- URE 1, is a flowdiagram showing the remaining formation of the sheet from the breakerstack to the fourth dryer section and to the final reeling operation.

With reference to the FIGURE 1, the refining of the pulp and theaddition of internal sizing agents and other wet end additives beforeapplication to the head boxes are in accordance with normal operationsfor the basis weight and caliper of the paperboard being produced. Theprimary head box, the secondary head box, the Fourdrinier, the firstpress, second press, first dryer section, third press, smoothing press,and second and third dryer sections are also operated in the same manneras they would be operated for a normal coated, cold waxing paperboard ofthe same basis weight and caliper. For example, a refined pulp ofapproximately one-half bleached pine and one-half hardwood pulp may beemployed that is refined to a Canadian standard freeness ofapproximately 500 ml. on the primary sheet from the primary head box anda freeness of approximately 275 ml. on the secondary sheet at thesecondary head box. It will be understood that the refined pulp includesthe usual internal sizing agents, and wet-end additives such as rosinsize, alum, or parafiin etc., for preparing conventional or normal,coated cold waxing board.

It will be understood that the ratio of pine (long fiber) and hardwood(short fiber) pulp may be varied considerably from the 1 to 1 ratio setforth. The use of hardwood pulp generally tends to make a smoother sheetsurface. Since the present invention relates to obtaining a greaseresistant paperboard by applying films to the sheet surface, it isdesirable to have as smooth a surface as possible. However, the ratio ofpine to hardwood in the grease resistant boards is not significantlydilferent from the ratio in the usual coated, bleached board grades.Sheet smoothness may be influenced by the amount and type of mechanicalrefining of the pulp. Although the presence of hardwood in the pulpcontributes to the grease resistance of the board, it is believed thatgrease resistant boards could be obtained by the practice of the presentinvention without the inclusion of hardwood in the pulp.

After the refined pulp is supplied to the primary head box and thesecondary head box, the pulp is applied to the wire of the Fourdrinier.The portion of the Fourdrinier wire table between the breast roll andthe suction boxes is considered to be the forming section on aredeposited on the machine wire as a result of suction which pulls thewater through the wire and deposits the fibers on the surface of thewire. Table rolls, suction boxes, and the suction couch roll are used onFourdrinier machines to aid in water removal and any increase in suctionat these points results in an increased rate of drainage and a morecompact sheet. From the wire, the sheet is transferred to the firstpress) in order to remove suflicient water from the fibrous mat to allowit to become sufiiciently self-supporting and to advance along themachine without rupture. After the sheet leaves the first press, it isadvanced to a second press of similar construction and then to a firstdryer section which is shown symbolically as a zigzag line in the FIGURE1.

After the sheet leaves the first dryer section it is advancedsuccessively through a third press, a smoothing press, a second dryersection and a third dryer section. The sheet is then about to enter thebreaker stack.

The breaker stack is employed during the manufacture of certain gradesof paper. The breaker stack is a tworoll stack and usually locatedapproximately one-half of the way along the dryer sections. The breakerstack smooths the paper while it still contains a high percentage ofmoisture and is most susceptible to calendering. As a result, the paperis appreciably increased in density, bursting strength and finish. Asalient feature of the present invention is the application of a highsolids cooked starch paste to the top surface and/or lower surface ofthe sheet of paperboard at this point.

Starch is used to a great extent for surface sizing and is cheaper thanmany other sizes such as animal glue. Most of the starch used in theUnited States is derived from corn, tapioca or potatoes. Starch is awhite to buff colored material which is available in powdered, pearl orcrystal form. Starch exists in the physical form of small grains orgranules, the size, shape and physical markings of which are sufiicientto identify the variety of starch. Chemically speaking, starch containstwo major chemical entities, amylose which is a straight-chain polymerof glucose and amylopectin which is a branched chain polymer of glucose,although certain waxy varieties of starch contain only amylopectin. Allstarches contain minor amounts of fatty acids, other lipids, proteins,and inorganic salts. Before starch can 'be used for surface sizing, itmust be heated in water and during the heating, the granules take onwater, expand, the granule commences to dissolve and disintegrate. Thedegree of granular disintegration and the viscosity of the starchsolution depend upon the type of starch, degree of modification, timeand temperature of heating, and amount of agitation.

A number of starches may be successfully employed with the inventionsuch as oxidized, dextrinized, hydrolized, esterified or etherified. Asan example, oxidized starch will be discussed in some detail. Oxidizedstarch is available in a wide range of viscosities by treating a slurryof native starch with alkalyn sodium hypochloride at a temperature nohigher than F. During conversion, soluble products are formed and theseare later removed by filtering and washing, after which the starch isdried and ready for shipment. A starch suitable for use in the practiceof the present invention is the thin boiling, oxidized starch known asFibersize by National Starch Products Incorporated, New York, NY.

Before the starch is suitable for coating the newly formed paperboard,it must be cooked. Approximately 1 part of starch is mixed with 4 partsof water and cooked by heating to a temperature in the range of to 210F. for approximately 15 to 20 minutes. It will be understood that thestarch-water mixture may be varied as set forth in the exampleshereinafter. Upon cooking, the starch forms a solution of improvedcolloidal properties compared to most other forms of modified starch.

The high solids cooked starch paste is now applied to the top surface ofthe sheet of paperboard just prior to the entry of the sheet into thenip of the breaker stack as shown on the FIGURE 1. Alternatively, thestarch coating may be applied to the lower or bottom surface only or toboth the upper and lower surfaces, as shown at the shower pipes A and/orB of the breaker stack in the FIGURE 1. A pool of the starch paste formson the surface of the sheet as the sheet enters the nip and ismaintained at a temperature in the range of 170 to 180 F. At that point,approximately one to one and one-half pounds per 1000 square feet ofpaperboard of cooked starch solids is applied to the surface of thesheet and impressed into the surface by the breaker stack. At this pointin the process, the oxidized starch tends to penetrate well into thesheet and form a surface film since the sheet of paperboard is stillrelatively wet and absorbent.

The manufacture of high grease resistant paperboard to which the presentinvention is directed, basically comprises the multiple application of arelatively highly concentrated cooked starch paste to the surface of thepaperboard on which the grease resistance is desired. As set forth, thefirst application of the cooked starch paste to the top surface or thebottom surface of the sheet of paperboard takes place at the breakerstack shown in the FIG- URE 1. At the breaker stack, a horizontal showerpipe indicated at A supplies the starch paste to the top surface of thesheet for application to the sheet of paperboard at the nip of thebreaker stack. Similarly, a lower shower pipe B supplies the starch tothe lower surface of the sheet. An excess of starch paste is applied sothat a pool of the starch paste exists where the sheet enters the nip ofthe breaker stack.

With reference to the FIGURE 2, after the application of the starchpaste to the top and/ or lower surface of the sheet at the breakerstack, the sheet goes through the fourth dryer section and then throughthe size press. The size press usually comprises two rolls between whichthe paper travels while it receives the surface sizing solution. Sizepresses may be of the vertical type or of the horizontal type. The sizesolution is sprayed on both sides of the sheet. At the size press,indicated on the FIGURE 2 by the reference figure B, a starch-claycoating is applied to both sides of the sheet. The coating mixtureapplied at the size press contains approximately to 22% total solids, ofwhich approximately one-half is clay and approximately one-half iscooked starch, the cooked starch being prepared in the manner previouslyset forth. The clay is the usual clay used in the manufacture ofpaperboard and may be of the air-floated or water washed type; however,the air-floated clay is preferable due to its a lower cost. The clay isusually mixed in water with the starch and it may be desirable to add asmall amount of rosin size. The clay disperses better in hot or warmwater than in cold so that it is compatible with the warm starchsolution.

After the sheet passes a size press of the FIGURE 2, it is advancedthrought the fifth dryer section and to the wet calender stacks. In theconstruction of a wet calender, a box extends across the length of thecalender roll and is used for holding the size or coating to be appliedto the paper. The solution to be applied is picked up by the calenderroll and applied to the paperboard surface. The lip of the box may befrom 2 to 4 inches below the nip of the roll and aproximately of an inchfrom the roll face with a flexible lip extending to the roll face. Thebox is arranged so that vertical and horizontal adjustments arepossible.

With further reference to the FIGURE 2, a coating is applied to both theupper and lower surfaces of the sheet at the wet calenders. To the topsurface of the sheet, a second application of the high solids cookedstarch paste is accomplished by means of a water box. This coating isapplied by the water box indicated by the reference C of the FIGURE 2.The reference D is a second water box and applies, to the bottom surfaceof the sheet, an application of lower solids cooked starch paste in therange of S to 10 percent solids. In addition, to the Water box referenceD, algin or alginic acid is added. A suitable quantity may be 1 part ofalgin for each 24 parts of starch. Algin or alginic acid is a highmolecular weight carbyl hydrate polymer of anhydro-BD-mannuronic acidwhich is obtained from a certain type of seaweed growing in quantity offthe West Coast of the United States. Alginic acid is insoluble in water,but it contains a high percentage of carboxyl groups which can bereacted with alkali to produce water-soluble salt known as alginates.Alginates can be dissolved readily in water by adding the dry product towater under vigorous agitation. Alginate is a filming-type sizing agentand tends to remain on the surface of paper when applied as a surfacesize. As in this application, it is used in combination with starches toproduce grease resistant paper-board where a high density-well-closedsurface is desired. Such an alginate is produced by Kelco, New York, N.Y., under the registered mark of Kelgin.

The temperature of the wet calenders in the area of the boxes C and Dmay be maintained at a temperature in the range of 170 to 180 F. Afterthe coatings are applied to the upper and lower surfaces of the sheet ofpaperboard at the wet calenders, the sheet is advanced to the firstcoater and air cap dryer of the FIGURE 2 where the third high solidscooked starch past is applied by the coater indicated at th referencefigure E. The temperature maintained at the first coater and air capdryer is somewhat lower than at the breaker stack or the wet calender,being in the range of to F.

As the sheet leaves the first coater it is advanced through the No. 1polisher and then to the second coater and air cap dryer where the lastcoating is applied. The second coater applies, at the reference numeralF, a normal pigmented coating which includes clay as the pigment withprotein as the binder, along with the necessary lubricating agents,deformers, etc. The normal pigmented coating may contain from 5 to 6parts of clay, 1 part of protein, and suflicient additives to insureproper flow characteristics.

As shown in the FIGURE 2, the sheet advances to the No. 2 polisher,through the dry calenders and is formed into a roll at the reelindicated at the end of the process line.

The following examples further illustrate the practice and principles ofthe manner in which the invention has been applied; however, theexamples are not to be construed as limiting the scope of the invention.

EXAMPLE I In this example, the operation of the paper machine tomanufacture highly grease resistant paperboard was similar to the methodof manufacturing a routine grade of a coated, cold waxing, bleachedpaperboard with the exception that a high solids cooked starch paste wasapplied to the'top surface of the sheet of paperboard at the breakerstack, the wet calenders and the first coater, as shown in the FIGURES 1and 2.

At the wet end, the pulp comprised approximately equal quantities ofpine and hardwood along with the usual wet end additives such as rosinsize, alum, etc. The Fourdrinier, first press, second press, first dryersection, third press, smoothing press, second dryer and third dryer arealso operated in the same manner as they would be for a normal coated,cold waxing paperboard of the same basis weight and caliper. The firstapplication of the high solids cooked starch paste to the top surface ofthe sheet of paperboard took place at the breaker stack. At this point,by means of a horizontal shower pipe, the starch paste is applied to thetop surface of the sheet. An excess of the starch paste is applied sothat a pool of the starch paste exists where the sheet enters the nip ofthe breaker stack. The temperature is maintained in approximately therange of to F. and approximately one to one and one-half pound per 1000square feet of paperboard of the cooked starch solids was applied to thesurface of the sheet and impresed into the surface by the breaker stackat this point in the process where the sheet of paperboard was stillrelatively wet and absorbent.

The cooked starch paste used for these applications was a pasteconsisting of approximately 20% solids of an oxidized, thin boiling orlow viscosity, starch. Prior to application on the surface of thepaperboard, the starch is prepared by adding approximately 4 parts ofcold Water by weight to 1 part of starch. The temperature is then raisedto approximately 195 F. and cooked for approximately 15 to 20 minutes.The starch is then ready for application to the surface of the sheet ofpaperboard at the breaker stack.

Following the application of the starch paste at the breaker stack, thesheet advances through the fourth dryer section and then to the sizepress. At the size press, FIGURE 2, a starchclay coating is applied toboth sides of the sheet. The coating mixture has from approximately 15to 22% total solids, of which approximately one-half is clay andone-half is cooked starch. This is a normal application for a coldwaxing grade of paperboard.

After the applications of the coating at the size press, the sheetadvances through the fifth dryer section and then through the calenderstacks, where a ditferent application is made to each of the sides ofthe sheet. To the top side of the sheet, the second application of thehigh solids cooked starch paste is made by means of a Water box. Thisstarch in preparation and composition is substantially identical to thatstarch applied at the breaker stack. To the bottom side of the sheet, anapplication of cooked starch paste of approximately 7% solids along withapproximately 1 part of an alginate for each 24 parts of cooked starchis accomplished of a water box. This is also normal application for acold waxing grade of paperboard.

After the wet calenders, the sheet travels through the first coater andair cap dryer. The first coater applies a coating of the high solidscooked starch paste to the top side of the sheet, which starch paste issubstantially identical to that applied at the breaker stack and the wetcalenders.

The sheet then passes through a polisher and then to the second coaterand air cap dryer. At the second coater, a normal pigmented coating wasapplied to the top side of the sheet. This coating employs clay as thepigment with protein as the binder, along with the necessary lubricatingagents, deformers, etc. The paper is then again polished, advancedthrough the dry calenders and is reeled at the output station.

The sheet of paperboard produced by the foregoing method was highlysuccessful in terms of grease resistance upon subsequent testing andobservation. The grease resistance tests consisted in applying aone-half inch head of cooking oil (such as Mazola oil) or turpentine tothe surface of the paperboard and measuring the length of time requiredfor the oil or turpentine to penetrate the paperboard and stain 50% ofthe under surface. Thecooking oil tests were terminated after six dayswith no penetration at all. The turpentine tests were terminated after30 hours with no penetration. In addition, the coatings of starch andother coating materials adhered well to the paperboard under conditionsof flexing and bending.

EXAMPLE II This run was substantially identical to Example -I exceptthat the breaker stack was turned off and the coating of starch at thebreaker stack was eliminated. The paperboard produced by this run had aturpentine test of hours and 20 minutes as compared with 30 hours of nopenetration when a coating of starch was applied at the breaker stack inExample I.

8 EXAMPLE III The purpose of this example was to make a runsubstantially identical to Example I to see if the results achieved inthe Example I could be reproduced. The highly grease resistantpaperboard was again produced and the tests showed approximately thesame imperviousness to oil and turpentine as that set forth in ExampleI.

EXAMPLE IV This run was conducted to establish the effectiveness of thegrease resistance of the paperboard by still applying three coats ofheavy starch paste as in Example I but applying a high solids coating atthe wet calender, the first coater and the second coater rather than atthe breaker stack, the wet calender and the first coater as the ExampleI. The product produced by this method showed a cooking oil test of 11minutes and a turpentine test of 240 seconds. Thus, the importance ofincreasing the grease resistance of the paperboard by applying a highsolids cooked starch paste at the breaker stack is demonstrated sincethe cooking oil test decreased from no penetration after six days ofexposure in the Example I to 11 minutes with stain of the under surfacein this example.

EXAMPLE V The purpose of this run was to determine the effectiveness ofwax and starch in the coating solutions. The conditions aresubstantially identical to those of Example IV except that a 10% wax wasadded to each of the high solids solutions. The cooking oil test wasalso terminated at 11 minutes with a 50% stain of the under surfacewhile the turpentine test decreased to 210 seconds.

EXAMPLE VI The purpose of this run is to establish the effectiveness ofproducing high grease resistant paperboard through the use ofhydroxyethyl ether starch instead of oxidized starches. The hydroxyethylether starch is of higher viscosity than the oxidized starches so theconcentration is reduced to approximately 7% solids starch (1 part ofstarch to approximately 13 parts of water) from the 20% solid starchsolution (1 part of starch to approximately 4 parts of water) employedin the foregoing examples.

The run is conducted in substantially the same manner as the run inExample I except for the substitution of the 7% hydroxyethyl etherstarch for the 20% oxidized starch of the earlier examples. Thepaperboard produced as a result of this process, is substantiallyidentical to the paperboard produced in Example I in regard to thecooking oil and turpentine tests.

EXAMPLE VII The purpose of this run is to establish an upper limit forthe starch concentration. The upper limit appears to be limited by thepumping equipment and other devices utilized for moving the starch tothe surface of the paperboard to be coated. In this run, the conditionsare substantially identical to those of Example I except that the starchconcentration is increased to 25% which is accomplished by mixingapproximately 1 part of starch by weight of 3 parts of water and cookingfor the prescribed time. Subsequent testing of the product produced bythis method showed results substantially identical to those obtained inExample I.

Thus, it has been determined that a high grease resistant paperboard canbe obtained through multiple applications of a relatively highlyconcentrated cooked starch paste to the surface of the paperboard onwhich grease resistance is desired. Further, it has been found that thegrease resistance of the paperboard has been enhanced to a high degreeof applying a coating of the high solids starch paste much earlier inthe m-anufavturing process than heretofore known, i.e., at the breakerstack and before the size press. The results are tabulated below and areillustrative of the degree of grease resistance obtained:

Application points of high solids starch in the process Holdout test(50% stain of under surface unless otherwise indicated) Cooking oilTurpentine Example 1:

(a) At breaker ac (b) At wet N o penetration after calender 6 days. Atfirst coatern. Example 11:

(a) At wet (b) g g agg ':}10 minutes hrs. 20 minutes. Example IV:

(a) At wet calender (b) At first 11 minutes 4 minutes.

No penetration after 30 hours.

(c) At second coater t What is claimed is:

1. In a process for manufacturing grease-resistant paperboard whereinthe sheet is formed in a conventional manner including the steps ofpressing, drying, smoothing and sizing, the improvement comprisingapplying a plurality of cooked starch paste coatings to the surface ofthe sheet, the first of the coatings being applied to the top surface ofthe sheet at a breaker stack while the sheet is in a wet and absorbentstate, and before the application of any other surface materials,applying a second coating of starch paste to the top surface of thesheet, and applying a coating of starch and aliginate to the othersurface of the sheet, and applying a third coating of starch paste tothe top surface of the sheet, each of the starch coatings applied to thesheet having a starch concentration of approximately 7% to 25%.

References Cited UNITED STATES PATENTS 1,195,888 8/1916 Wheelwright162-175 2,036,422 4/1936 MacLaurin 162-184 2,170,272 8/1939 Walsh162-175 X 2,214,641 9/1940 Massey et a1 162-175 2,324,529 7/1943 Musher162-175 2,378,113 6/1945 Van de Carr 162-184 X 3,219,519 11/1965 Barberet a1. 162-175 S. LEON BASHORE, Primary Examiner.

